No present-day research and development program is complete without the inclusion of a robust modeling and numerical simulation component. Models and model-based numerical simulations are extensively used to probe complex materials behavior and structure in order to obtain a deeper insight into the fundamentals of materials. Multi-physics models are becoming increasingly common, with advances in computational science, and are rapidly advancing the basic understanding of materials.The aim of this special collection: "Theory, Modeling and Numerical Simulation of Multi-Physics Behavior", with its 25 selected and peer-reviewed papers, is to highlight the theories, models and numerical techniques that have permitted multi-physics simulations to become an integral part of research and development programs.